Documentation, Build/publish workflow and metatag fixes

[luigimannoni]

This PR targets the drive-realtime-deprecation wip branch with the following:

• Changes the build and deploy gulp tasks, now gulp deploy will build the project prior to deploying to gh-pages, gulp build will only build the files exiting after finishing the task, gulp dist will still work as usual
• Adds npm run build npm run deploy commands
• Adds few additions to CONTRIBUTING.md on the pngquant npm package plus few extras
• Fixes og:ulr typo on metatags => og:url